The invention relates to a loading platform system for mounting on vehicles, especially trucks, comprising a lifting mechanism, an essentially plate-like loading platform for lifting and lowering a load and at least one lift actuator for lifting and lowering the loading platform. The lifting mechanism includes at least one support arm with a first end by which it is supported on the vehicle so as to be pivotable about a first axis of rotation and a second end which is connected pivotally to the first end of a lifting actuator, a second end of the lifting actuator being rotatably supported on the vehicle.
Such a loading platform system is described for example in EP-A-0808747. Loading platform systems have been known in various designs for a long time. They are often used on trucks in order to be able to unload loads carried by the trucks at the destination that is to lower a load from the truck bed to the ground so that the load can then be further moved by other means. The same is true for the loading procedure of a vehicle that is the load is first deposited on the loading platform when disposed at ground level and lifted to the level of the vehicle load bed and finally moved onto the load bed.
In some designs of loading;platform systems, the loading platform is tilted from a horizontal to a vertical position when the loading procedure is completed. In this position, the loading platform can serve additionally as the rear end wall of the load bed or respectively, of a box-like loading space.
In other embodiments of known loading platform systems, that is, so-called folding loading platforms, the loading platform is not tilted from a horizontal to a vertical position and vice versa; rather these loading platforms are folded after the loading procedure and are then moved below the load bed that is below the rear end of a load bed of a truck.
For the lifting and lowering of the loading platform while in a horizontal position for loading a load onto, and unloading a load from, the loading bed of a truck to street level and from the street level to the level of the load bed of the truck, a so-called lifting actuator is utilized which is operated hydraulically, pneumatically, electrically or in some other way. For the tilting of the loading platform, if such possibility is provided, that is, for the opening and closing of the loading space by movement of the platform from the vertical to the horizontal position and vice versa, a tilting arrangement is used which is actuated hydraulically, pneumatically, electrically or in some other suitable way. Loading platform systems of the type described have at least two actuator arrangements, wherein generally the lift actuator arrangement cooperates with one support structure of a lift and tilting structure which is usually, but not necessarily a parallelogram arrangement. The tilting actuator arrangement cooperates with the other support structure of the lift and tilting structure. However, a tilt actuation structure is only provided if a tilting movement from a horizontal position of the loading platform to the vertical positions and vice versa is necessary.
Known loading platform systems encountered substantial problems during loading and unloading that is under the effects of a force which may reach substantial values depending on the weight of the goods to be moved: As a result of the load disposed on the loading platform, the loading platform may bend relative to the loading bed of the truck so that gaps are formed between the loading platform and the load bed in horizontal as well as in vertical directions. Furthermore, those gaps may vary over the width of the load bed opening. As a result, particularly with heavy loads which need to be moved by the loading platform, vertical thresholds are formed between the loading platform and the loading bed so that the load must often be moved across such threshold by a carriage by hand or by other means.
With the solution presented in EP-A-0 808 747 of the assignee of the present invention, the problems described above have been solved that is no vertical or horizontal gaps between the loading platform arranged horizontally relative to the loading bed of a motor vehicle are formed. In addition, the solution has the very positive effect that the loading platform may be very simple in design, and, because of its design, does not provide for an uneven loading of the support structure. As a result, the support structure remains operative over a long period of time and the service requirements could be reduced to a minimum.
In a lifting support structure of such a loading platform system a substantial torque is generated on the lift support mechanism when the loading platform is in a horizontal position already because of the relatively high weight of the loading platform. Consequently, there is a force effective on the support structure with a substantial vertical force component. When the support structure reaches its end position at the level of the loading bed of the truck that is at the maximizing lift travel of the loading platform and the maximizing lift effect of the lift actuator structure, there is still a small vertical threshold between the level of the loading platform and the level of the load bed of the truck. In this respect, it is pointed out that the lifting mechanism with the support arm and the lift actuator including the pivot or, respectively, axis points of the loading platform can actually not be a totally rigid system since, because of design and material reasons, there is always a certain elastic deformation of the individual elements of the lift mechanism. The elements of the lift mechanism therefore act in a way like springs, particularly the support arms. In order to overcome the deformation caused by the spring action which is responsible for the forming of the gap described earlier the lift actuation arrangement is so operated that the loading platform is lifted actually to the same level as the loading bed of the truck so as to overcome deviations caused by the elastic deformation particularly of the support arms of the lifting mechanisms in order to reduce any gap between the loading platform and the loading bed to zero.
This problem is solved by the loading platform system de scribed above in an elegant manner by providing a second support arm which, at its first end, is interconnected with the first support arm and has at its second end, a pivot axis which extends essentially perpendicularly to the two support arms and by way of which the second support arm is rotatably connected to the loading platform. With the two support arms which are interconnected like pincer arms or spring pliers, the lift actuator operation or movement can be completed by way of the spring action of the two support arms until the loading platform reaches the level of the loading bed while the elastic deformation of the lift mechanism is compensated for.
This design is however relatively expensive and complicated although it is very effective.
It is therefore the object of the present invention to provide a loading platform system, whereby the loading platform can be raised in a simple manner exactly to the desired level so that no vertical gap is formed between the loading platform and the loading bed no matter how large the load on the loading platform is. The system should also be easily installable in existing loading platform arrangements.
In a loading platform system for mounting on a vehicle, comprising a lift mechanism support structure, at least a first support arm having an end pivotally connected to the lift mechanism support structure and pivotally supporting at its other end a loading platform for supporting a load and a lifting actuator connected between the lift mechanism support structure and the other end of the support arm for operating the support arm for lifting and lowering the loading platform, the loading platform is pivotally connected to the second end of the first support arm by way of a spring-loaded guide member, which is movably disposed in an opening formed in a guide element mounted on the support arm at the other end thereof.
With the arrangement according to the invention a spring action between the second end of the support arm and the respective pivot shaft of the loading platform is provided in a simple manner. There is no need to manufacture the lifting mechanism from highly stressible expensive materials so that these parts, especially the lifting arms can be manufactured relatively inexpensively. In addition, the solution according to the invention has the advantage that the elasticity modules required for a particular application can be accommodated in a simple manner by a suitable selection of the spring means without the need for changing the design of the lifting mechanism, especially the support arms. The solution proposed by the present invention can also be realized in a simple manner.
As spring means, any type of spring may be utilized such as rubber springs, tension springs, leaf springs spiral springs, torsion rod springs coil or coil cone springs or air strut springs. Preferably, however, a compression spring is used or, in another advantageous embodiment of the loading platform system, a hydraulic and/or pneumatic spring is utilized.
In order to ensure in a simple manner that between the pivot axis of the loading platform and the respective second end of the support arm the smallest possible horizontal play with respect to the plane on which the vehicle with the loading platform system is disposed, is achieved, the loading platform system is preferably so designed that the spring means is effective between a guide structure disposed at the second end of the support arm and a guide element which is disposed in an opening of the guide structure so as to be movable back and forth therein. The guide structure and the opening in the guide structure which serves as the direct guide means for the guide element which is movably disposed therein may have any shape that is rectangular cross-sections of the opening and of the guide element are possible. However, the guide element may also be movably disposed in a guide opening, which has a circular cross-section.
At the end of the guide element remote from the guide structure, there is preferably provided a shaft element whose axis forms the pivot axis of the loading platform. In this way, it becomes advantageously possible to form the guide element and a sleeve forming a shaft as a single element defining the axis rotation for the loading platform. But it is also possible to provide, at the remote end of the guide structure, a shaft bolt which extends into correspondingly formed openings or sleeves in the loading platform.
Since a loading platform system is generally mounted on a vehicle where it is subjected to a rough environment that is to moisture, dust and other ambient contaminations, sometimes snow and ice, also salt as it is spread on the streets in winter, it is advantageous to enclose the spring means in a protective enclosure which can be rapidly exchanged if it should become brittle, damaged or otherwise unuseable.
The protective enclosure may be for example an elastic bellows of an elastomer material such as rubber or plastic.
The support arm of the loading platform system does not need to comprise a single arm. It may be advantageous to provide two arms arranged in parallel spaced relationship. In this way, the stability of the support arm arrangement may be improved in a simple manner. The support arm itself may have any suitable cross-section, that is, it may be circular and/or plate-like. If the support arm is tubular or the two spaced support arms are tubular, commercially available tubes may be used for the manufacture of the support arms whereby manufacturing of the arms is simplified and their costs are reduced.
The situation is similar for support arms, which are essentially plate-like. Thin plate-like unfinished structures may be used from which the arms can be stamped out or cut out.
In order to improve the stability of the support arms in an embodiment wherein the support arms are formed by two spaced support arm elements the support arm elements are preferably interconnected by at least one bracing structure.
Below the invention will be described in greater detail with respect to a particular embodiment on the basis of the schematic drawings.